Synthesis Of Ionic Liquid Materials Containing Transition Metal Ions And Their Absorption And Separation Properties Of Organic Pollutants

In the petrochemical industry,ethylene（C₂H₄）is one of the most critical chemical raw aterials in the plastic chemical industry,and it is a symbol to measure a country’s petrochemical level.There are a lot of ethylene resources in refinery dry gas,but it is accompanied by ethane（C₂H₆）with similar physical and chemical properties（molecular radius,dipole moment and boiling point,etc.）.However,low temperature distillation,which is often used for C₂H₄/C₂H₆ separation,has high energy consumption.And it is still challenging to obtain high-purity C₂H₄ gas.The solvent absorption method is a mature technology and is widely used in gas separation.As a green absorbent,ionic liquids（ILs）have the advantages of good thermal stability,gas solubility and designable structure,which provide a new idea for gas recovery and utilization.Silver nitrate aqueous solution is the most widely used absorbent in industry,but it has the disadvantages of low activity of Ag⁺and low absorption of C₂H₄.Here,several silver-based ionic liquids（Ag-ILs）were prepared by ionic liquids（ILs）,silver salts and ethylene glycol（EG）.Absorption experiments of pure gas and mixed gas were carried.And the effects of various anions and cations of ILs,molar ratio of ILs to silver salt,and EG ratio on absorption performance and recirculation of absorbent were investigated.Due to the synergistic effect of ILs,EG and Ag+,the absorption of C₂H₄ in Ag-ILs absorbent[Emim][BF₄]/Ag BF₄/EG（2:1:0.1）is as high as 102.6 mg/g（2.19 mol C₂H₄/mol Ag⁺）,which is higher than most absorbents,and the highest selectivity is 37.8.In addition,the absorption performance remains stable after 5 cycles of absorption and desorption.The mechanism of interaction between Ag-ILs and C₂H₄ was studied through NMR and FTIR.ILs and EG synergistically weaken the electrostatic effect between the anions and cations of Ag BF4,and increase the silver salt activity to enhance the absorption of C₂H₄.It is expected that Ag ILs will become a new medium with commercial potential for C₂H₄/C₂H₆ separation.However,the instability of silver salts under light is an important factor limiting the industrial application of Ag-ILs.Therefore,the double-silver salt ionic liquid was prepared by using ionic liquid and two kinds of silver ions to improve the stability of Ag-ILs.The results showed that Ag NTf₂ anions aggregated near Ag⁺,which protected Ag⁺and enhanced the stability of the double-silver salt ILs.Furthermore,the introduction of Ag BF₄ into[Emim][BF₄]increased the binding sites of C₂H₄ and restricted the solubility of C₂H₆,thus enhancing the sieving ability of Ag-ILs and significantly increasing the uptake rate of C₂H₄.The positive effect of these two factors endows the double silver salt ionic liquid with a high C₂H₄absorption capacity（89.88 mg C₂H₄/g absorbent）,but also exhibits excellent stability and has great potential for direct separation of C₂H₄/C₂H₆.In order to reduce the cost of Ag-ILs absorbents,cheap transition metal salts such as Al and Zn were used to replace Ag salts to achieve high absorption and low absorbent cost.Therefore,bimetallic salt ILs were prepared from ILs,Ag⁺and Al³⁺.In Ag-ILs,Al³⁺binds Al（OTf）₄^-with the anion of Ag OTf through a unique covalent bond effect,which weakens the electrostatic effect between the anion and cation of Ag BF₄ and significantly improves the activity of Ag⁺and high C₂H₄ affinity of Ag-ILs.The respective absorption properties of C₂H₄ and C₂H₆ in bimetallic salt ionic liquids were studied,and the absorption of C₂H₄ increased from 22.42mg/g（1.04 mol C₂H₄/mol Ag⁺）of[Emim][OTf]/Ag OTf（4:1）to[Emim][OTf]/Ag OTf/Al（OTf）₃（8:1:1）of 27.87 mg/g（1.76 mol C₂H₄/mol Ag⁺）,the absorption capacity of its silver salt increased by 69%.This work provides a promising material for C₂H₄/C₂H₆ separation process.This study provides several new ideas for the design of C₂H₄/C₂H₆ separation materials,and Ag-ILs are expected to become one of the most competitive absorbents in the field of ethylene/ethane separation.